1. Field of the Invention
The present invention relates to a roof assembly for a building structure, and more particularly, but not by way of limitation, to roof assembly improvements providing greater load bearing and water tightness capabilities.
2. Discussion
Numerous types of roof assemblies have been proposed for pre-engineered buildings to provide adequate load resistance and watertightness, while expanding and contracting to accommodate variations in weather conditions. Typical of such roof assemblies, the standing seam roof assembly has become popular in recent years.
The panel members of a standing seam roof assembly are joined along lapped together side edges forming the standing seams and are secured to secondary structural members either by fasteners, such as screws, that extend through the panels (often referred to as ‘through fasteners’), or by clips. Through fasteners, when used, extend through flat portions of the panels to attach to the underlying support structure to substantially lock the panels and support structure together, limiting differential movement between the panels and support structure. Clips used with standing seam roof assemblies connect to the panel edges and are either floating (one or two piece moveable) or fixed (single piece with no movement allowed between the panel and the supporting structure).
Roofs are generally classified either as shed roofs or low slope gasket roofs. Shed roofs are designed to shed water by gravity pulling the water down and away from panel joints more effectively than wind or capillary action propel water through the joints, and such roofs generally have slopes of three to twelve or greater. Gasket roofs, on the other hand, are generally low sloped and have roof joints that are made watertight by sealant material in the panel joints. Securing the sealant material in place is accomplished, for example, by encapsulating or by exerting pressure on a gasket material, such as by seaming. Generally, low slope gasket roofs have slopes as low as one quarter to twelve.
Heretofore, field seamed gasket joints in large roofs have generally been limited to two-piece clips in which movement between the roof and the underlying structure occurred within the clip. The reason for this is that, in the past, the top hook portion of the clip intersected the gasket sealant, and if the clip hook moved in relation to the panel which held the sealant, the movement of the clip hook deformed and destroyed the gasket seal. Single piece clips have been used freely in shed roofs where gasket sealing is not required.
Standing seam metal roof panels exhibit considerable diaphragm strength, and it is desirable to use this strength by interconnecting the panels side to side so that adjacent panels do not slide relative to each other; further, the panels are connected to the support frame to stabilize the support frame, rather than bracing and stabilizing the support frame by other means. In the past, stabilization of the support frame has been achieved by means of separate bracing. On gasket roofs, two-piece floating (moveable) clips, in some instances, have been used to permit the brace and frame to remain fixed while permitting panel movement relative to the frame, such as due to temperature and other gradients. Alternatively, when fixed clips are used, the length of the panel run is limited to about 40 feet so that the expansion and contraction of the panel does not damage the connections to the underlying support structure.
The desirable result of eliminating detrimental differential movement between the panels of the roof assembly and the support structure on large roofs can also be achieved by constructing the underlying support structure with the capability to move slightly to accommodate expansion and contraction of the roof assembly. One means of achieving this is exemplified by the Flex Frame™ support system produced by ReRoof America, Inc. of Tulsa, Okla.
The interconnected panel members of a standing seam roof assembly lend stiffness and strength to a flexible roof structure, while allowing the roof structure to expand and contract as a function of the coefficient of expansion of the panel material and the temperature cycles of the roof panels.
If floating clips or flexible framing are not used, the repeated action of expansion and contraction of the panel member will, in time, weaken the panel-to-panel lap joints and the panel to framing connection, causing separation, structural failure and roof leakage. Leaks are generally caused by the weakening of the fastening members and working or kneading of the sealant disposed at the joints. Thus, prior art sealants for standing seam roof assemblies have required the qualities of adhesion, flexibility and water repellence. Further, in many instances the pressure on the sealant can vary greatly throughout the length of the panel sidelap and end lap joints, resulting in uneven distribution and voids in the joint sealant.
Many problems encountered with prior art standing seam roofs, such as structural failures and leaks, are overcome by the standing seam floating roof assembly taught by U.S. Pat. No. 5,737,894 issued to Harold G. Simpson. Adjacently disposed panels are joined by interlocking female and male sidelap members to form a standing seam assembly, or joint, and clips connect the standing seam joints to underlying building support structure, with upper portions of the clips hooked over the male sidelap members and the lower portions attached to the underlying building supporting structure, such as a purlin or joist.
Floating clips of the sliding type permit clip hook portions to move relative to clip base portions connected to the underlying building supporting structure, while the clip hook portions are secured to the panel sidelaps. A sealant material is positioned between the interlocking joints of interlocked female and male sidelap portions of the panels, forming a sealant dam to make the joints watertight.
In addition to new construction, standing seam roof assemblies are also finding increased usage in another segment of the roofing industry, the replacement of built-up roofs. Generally, a built-up roof is formed of a plurality of interconnected sections that are sealed by a watertight over-coat of asphaltic composition. Built-up roofs have generally performed well, but problems occur with age, with building settlement and with standing water pockets resulting from construction errors. Standing water causes roof deterioration, resulting in leaks and other problems.
A need has long existed for replacing a roof without making substantial modifications to the existing roof. In addition to economy of fabrication and ease of on-site construction, it is desirable that a newly erected roof assembly present a new roof surface independent of the variations in the surface of the preexisting roof Past roof replacements, especially those capable of altering the roof slope to improve drainage, are excessively time consuming and require both substantial destruction of the original roof and extensive custom construction, exposing the building and its contents to damage by the elements roof replacement.
The process of manufacturing standing seam panels results in dimensional variations occurring in such panels, and this is especially of concern when the width of the panels vary significantly beyond specified tolerance limits. Since the edges of the panels that form the male and female sidelaps are interconnected and mechanically joined, the standing seams of interlocked adjacent roof panels must accommodate panel width variations. This is especially true when the width dimension of panels exceed the specified maximum permitted width, as the excess material can cause difficulty in joint formation. That is, when the edge of the panels extend beyond the design specification, the extra long leg components of a sidelap in the standing seam can interfere with uniform joint closure and sealing, resulting in poor quality seams.
In addition to the other deficiencies of the prior art mentioned above, there is a need for accommodation of dimensional variations of roof panels used to form standing seam roof assemblies.